The present invention relates to a process and apparatus for the refining of melts by means of a pulverous solid material or a gas or both.
A pulverous reagent and a molten melt have previously been mixed with each other by many different methods, e.g. by injecting a pulverous reagent into a batch of molten metal in a ladle through a tuyere fixed to the ladle wall below the melt batch surface or through a tuyere formed at the base of the ladle. Surface injection lancets have also been used for injecting a pulverous reagent at a high velocity under the surface of a melt batch in the ladle or by pushing an injection lancet into a hot melt batch in the ladle and by injecting a pulverous reagent under the surface of the melt.
In the injection methods first mentioned, the mixing efficiency has, however, been rather low. Attempts have been made to improve it by using surface injection and very small-diameter nozzles in order to inject a pulverous material and a carrier gas into the melt at a high velocity, but in this case the powder has quickly worn out the nozzles. For this reason, lancets have been immersed in the melt; the lancets have been made straight and with a large diameter, in which case large non-dispersing gas bubbles are, however, produced in the melt, and solid material may rise to the melt surface inside these bubbles, without coming into contact with the melt. Furthermore, large bubbles cause strong agitation of the surface.
Also known is a mixing method in which a pulverous reagent is injected from above through a lancet lowered into the melt while melt is poured into the ladle. In this case the turbulence of the melt in the ladle promotes the mixing of the reagent with the melt. The lancet cannot, however, be lowered too close to the bottom of the ladle without the pulverous material beginning to cause wear of the ladle bottom. Even in this case there is splashing in the melt; this splashing can, however, be diminished by using the special nozzle disclosed in Finnish Patent Application No. 3167/74, which is, however, more expensive than an ordinary lancet.
The object of the present invention is thus to provide a method and apparatus for an effective and rapid mixing of a pulverous reagent and/or a gas with a hot melt without high injection velocities and resulting rapid wear of the nozzles and without significant melt surface agitation or splashing.